system : an instance of the LTI class or a tuple describing the system.

The following gives the number of elements in the tuple and
the interpretation:

2: (num, den)

3: (zeros, poles, gain)

4: (A, B, C, D)

U : array_like (1D or 2D), optional

An input array describing the input at each time T. Linear
interpolation is used between given times. If there are
multiple inputs, then each column of the rank-2 array
represents an input. If U is not given, the input is assumed
to be zero.

T : array_like (1D or 2D), optional

The time steps at which the input is defined and at which the
output is desired. The default is 101 evenly spaced points on
the interval [0,10.0].

X0 : array_like (1D), optional

The initial condition of the state vector. If X0 is not
given, the initial conditions are assumed to be 0.

kwargs : dict

Additional keyword arguments are passed on to the function
odeint. See the notes below for more details.